The process of xerography, as disclosed by Carlson in U.S. Pat. No. 2,297,691, employs an electrophotographic element comprising a support material bearing a coating of an insulating material whose electrical resistance varies with the amount of incident electromagnetic radiation it receives, such as during an image-wise exposure. The element, commonly termed a photoconductive element, is first given a uniform surface charge, generally in the dark after a suitable period of dark adaptation. It is then exposed to a pattern of actinic radiation which has the effect of differentially reducing the potential of this surface charge in accordance with the relative energy contained in various parts of the radiation pattern. The differential surface charge or electrostatic latent image remaining on the electrophotographic element is then made visible by contacting the surface with a suitable electroscopic marking material. Such marking material or toner, whether contained in an insulating liquid or on a dry carrier, can be deposited on the exposed surface in accordance with either the charge pattern or discharge pattern as desired. Deposited marking material can then be either permanently fixed to the surface of the sensitive element by known means such as heat, pressure, solvent vapor or the like, or transferred to a second element to which it can similarly be fixed. Likewise, the electrostatic charge pattern can be transferred to a second element and developed there.
Since the introduction of electrophotography, a great many organic compounds have been screened for their photoconductive properties. As a result, a very large number of organic compounds have been known to possess some degree of photoconductivity. Many organic compounds have revealed a useful level of photoconduction and have been incorporated into photoconductive compositions. Among these organic photoconductors are certain of the triphenylamines as described in U.S. Pat. No. 3,180,730 issued Apr. 27, 1965, and the polyarylalkane compounds such as those described in U.S. Pat. No. 3,274,000 issued Sept. 20, 1966; U.S. Pat. No. 3,542,547 issued Nov. 24, 1974; and in U.S. Pat. No. 3,615,402 issued Oct. 26, 1971. It has been a continuing objective to find new photoconductive materials and new photoconductive compositions.
Certain such materials, however, may exhibit photoconductivity only under certain circumstances, as when in single crystal form. In one such instance, Kleinerman et al, in an article entitled "The Photoconductive and Emission Spectroscopic Properties of Organic Materials" which was presented at the International Conference on Luminescence at the New York University on Oct. 10, 1961, reported that no photoconductivity was observed in a solid polystyrene solutions which contained 20 percent 1,1,4,4-tetraphenyl-1,3-butadiene, which is a good photoconductor in the pure crystalline state. The above is found on page 219 of the published proceedings of the Conference in the book Luminescence of Organic and Inorganic Materials, edited by Kallman and Spruch, John Wiley & Sons, Inc., New York, 1962.